Fundamental research on discharge characteristics and reaction kinetics of corona ignition

Abstract

The development of gasoline engines has been continuously aimed at the reduction of fuel consumption and hazardous emission. Future high-efficiency engines would require advanced combustion processes, but the technological approaches could have adverse effect on the ignitability of air-fuel mixture. In order to overcome these limiting factors, various alternative ignition systems have been recently tested to replace the conventional spark ignition. Among them, corona ignition, which is based on the non-thermal plasma discharge phenomenon, is recognized as a promising solution. The effect of using corona ignition has been already studied by several researchers

however, the most fundamental information on the streamer formation as well as the influence of in-cylinder charge motion are still to be discovered for the optimization of the combustion process. In this work, the variation of discharge morphology and the reaction kinetics with different boundary conditions were investigated in atmospheric air using high-speed imaging and optical emission spectroscopy. Results of both experiments showed that strong flow field near an ignitor electrode reduced the discharge intensity. In a highly turbulent flow, the intensity decreased substantially as well as the shape of streamers were strongly distorted. The variation of spectral intensity measured from the emission spectroscopy was in a good agreement with that of luminous intensity. The corona ignition showed the potential of generating free OH radicals at room temperature in the existence of water vapor. By using spectroscopic temperature measurement methods, the rotational temperature was calculated. The gas temperature of corona discharge lied lower than the plasma temperature of the conventional spark ignition, and it corresponded well to the temperature range of a non-thermal plasma.